This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Many Gram-negative plant and animal pathogens depend on a Type III protein secretion system (TTSS) that injects proteins called effectors into eukaryotic cells, to cause disease. Although all effectors contain N-terminal secretion signals, a subset require the binding of specialized proteins, type III chaperones (TTCs), to become secretion competent. Much research has been carried out on TTCs, but their essential function remains a matter of controversy and studying this topic will promote our understanding of TTSSs and may allow for novel strategies to control plant and animal diseases caused by TTSS-containing pathogens. Experiments outlined in this proposal are designed to explore the role chaperones play in the TTSS system of Pseudomonas syringae by investigating the contribution of TTC-binding domains to effector secretion and translocation, by determining protein interactions between TTCs and effectors and/or the secretion apparatus proteins, and by exploring whether TTCs contribute to regulation of this secretion system.